The present invention relates to improvements in solid-fuel burning stoves, and particularly to an improved latch for a door to the combustion chamber of such a stove.
Stoves which burn wood, coal, or similar solid fuels have long been used for cooking and for heating dwellings. Because of continually increasing costs for fuel, numerous efforts have been made to improve the efficiency of fuel use in these stoves. The pot-bellied stove once common in the parlor drew its combustion air from the room in which the stove was located. A damper, located usually in the stove pipe leading to the chimney flue, and an air inlet register, usually located in the stove front, provided some control of the amount of air admitted to the combustion chamber of the stove, but the stove was far from airtight, and a large volume of already heated air from the space surrounding the stove was drawn into the stove and used to burn the fuel. Thus, this heated room air was exhausted up the chimney and was lost.
Recently developed heating stoves use a substantially airtight combustion chamber and efficient air supply control dampers to overcome the aforementioned shortcoming of these stoves by limiting the amount of combustion air admitted to the fire to a small portion of that which would have been drawn into non-airtight stoves. The result of this construction is that combustion of fuel within the stove is limited by the amount of oxygen contained in the restricted supply of air admitted to the combustion chamber. The temperature of fuel within such a stove often far exceeds the ignition temperature of the fuel, but when the air supply control damper of the stove restricts the air supply, the fuel can burn only at a reduced rate. This provides better control over utilization of the fuel, since a smaller proportion of the heat liberated by combustion of the fuel is allowed to escape through the chimney, allowing more of the heat produced by combustion of the fuel to be conducted through the stove and radiated into the rooms being heated by the stove than is possible with non-airtight stoves.
While improving economy, this provision does have associated significant problems. A door to the combustion chamber is still necessary to allow placement of fuel in the combustion chamber, and when the door is opened, unless it is moved very slowly, a low pressure zone is created behind the door which may pull smoke and flame outward from the stove into the room.
Another related problem, particularly if the stove contains fuel whose temperature is above its ignition point but which has previously been prevented from burning because of air starvation, is that free admission of oxygen to the combustion chamber when the stove door is opened may result in nearly explosive ignition of the flammable gaseous portions of the fuel present within the combustion chamber. This extremely rapid ignition, known as backpuffing, presents a risk of burn injury of the person opening the stove door as the burning gases rapidly expand.
A partial solution to this problem is to always allow air to freely enter the combustion chamber by opening the air supply register before opening the door. However, this procedure entails an additional step which the user must remember each time the door is opened. A better solution is to eliminate the possibility of opening the stove door too rapidly by providing a latch which necessitates a two step door opening procedure. If the door is first opened a small distance so that air is allowed to enter the combustion chamber for a short time, this additional combustion air which is allowed to enter the firebox does so gradually enough to burn the fuel without an explosive effect. The flame, smoke, and other gaseous products of combustion are then able to re-establish or follow the normal convective pattern and be exhausted through the stove pipe and chimney flue. This procedure particularly eliminates the possibility of flame or smoke being sucked or explosively forced into the room in which the stove is located.
In the past, however, no means of requiring this procedure has been provided in stoves. Stoves have been equipped typically with simple latches which hold the doors in their normal closed positions. When released, such latches simply allow the doors to be opened fully, but make no requirement for hesitation with the door slightly ajar.
Jennings, Jr., U.S. Pat. No. 2,970,718 discloses a latch for a door of a sterilizer which may have an interior pressure greater than atmospheric pressure. The latch disclosed by Jennings prevents opening of the sterilizer door so long as the pressure within the sterilizer is above atmospheric pressure, by requiring the door to be pressed inwardly against the pressure in the sterilizer to allow a shoulder in one portion of the latch to clear the top of a keeper before the latch may be further rotated to completely release the door. While this latch provides a two step door opening procedure the first step does not provide movement of the door away from the mating surfce of the doorway to allow admission of air. Thus use of this type of latch on a door of a solid-fuel stove would not serve the desired function.
What is required, therefore, is a latch for a combustion chamber door of a solid-fuel stove which requires the door to hesitate in a partially opened position before it may be fully opened.